Power tools, such as electric circular saws and grinders, are required to brake their motors and quickly stop their end bits for workability when their trigger switches are turned off.
As illustrated in FIG. 1, in a conventional power tool 201, when a trigger switch 202 is turned on, a power supply 203 forms a closed circuit together with an armature 204 and a field coil 205 to rotate the armature 204 to move an end bit. The armature 204 and the field coil 205 constitute a motor. When the trigger switch 202 is turned off, the armature 204 is disconnected from the power supply 203, and forms another closed circuit together with a brake coil 206. In this time, the current which flows in the brake coil 206 brakes the rotation of the armature 204, and stops the end bit.